The photonic time-stretch technique allows electric field pulse shapes to be recorded with picosecond resolution, at megahertz acquisition rates. Using this strategy, we could directly record spatial patterns that spontaneously appear in relativistic electron bunches, and follow their dynamical evolution over time. We present recent results obtained using two strategies. At SOLEIL, we present the shapes of the THz pulses which are emitted by the structures, and detected far from the emission point, at the end of a beamline. At ANKA, we present how it has been possible to monitor directly the electron bunch near-field. These new types of single-shot recordings allow direct and stringent tests to be performed on electron bunch dynamical models in synchrotron radiation facilities.

We present the first direct single-shot recordings of optical rogue waves by using a homemade Time Microscope having a temporal resolution of 250fs (P. Suret et al., Nature Communications 7, 13136 (2016)). In our experiments, partially coherent waves emitted by a amplified spontaneous emission light source experience nonlinear propagation in a single mode optical fibre. Experimental observation reveal the emergence of coherent structures embedded in the random waves. The probability density function of optical power is found to evolve from exponential distribution that corresponds to linear superposition of waves to heavy tailed distribution. The experiments are very well reproduced by numerical simulations of the one dimensional nonlinear Schrdiner Equation.

The multi-soliton complexes are induced in a common broadband commercial laser oscillator (~10 fs pulse width) by applying external perturbations. The optical spectrum of a multi-pulse complex corresponds to a spectral interferogram, encoding both the distances and the relative phase of its constituents. In order to access this information for fast bound-state dynamics, rapid spectral detection is essential. The presented single-shot spectroscopy is enabled via the transformation of spectral information to the time-domain via group-velocity-dispersion in a long optical fiber, and subsequent high-bandwidth real-time acquisition [1]. By recording such single-shot spectral interferograms, we can resolve a diverse set of dynamic bound-states, and identify unprecedented rapid dynamics of bound-states with regular, periodic and aperiodic behavior in a state-of-the-art broadband Kerr-lens oscillator.

We have experimentally reported on a real-time single-shot spectroscopy of a broadband Yb-doped fiber (YDF) laser which based on a nonlinear polarization evolution by using a time-stretched dispersive Fourier transformation technique. We have measured an 8000 consecutive single-shot spectra of mode locking and noise-like pulse (NLP), because our developed broadband YDF oscillator can individually operate the mode locking and NLP by controlling a pump LD power and angle of waveplates. A shot-to-shot spectral fluctuation was observed in NLP. For the investigation of pulse formation dynamics, we have measured the spectral evolution in an initial fluctuations of mode locked broadband YDF laser at an intracavity dispersion of 1500 and 6200 fs2 for the first time. In both case, a build-up time between cw and steady-state mode locking was estimated to be 50 us, the dynamics of spectral evolution between cw and mode locking, however, was completely different. A shot-to-shot strong spectral fluctuation, as can be seen in NLP spectra, was observed in the initial timescale of 20 us at the intracavity dispersion of 1500 fs2. These new findings would impact on understanding the birth of the broadband spectral formation in fiber laser oscillator.

Modulation instability is a fundamental process of nonlinear physics, leading to the unstable breakup of a constant amplitude solution of a particular physical system. There has been particular interest in studying modulation instability in the cubic nonlinear Schrödinger equation (NLSE) which models a wide range of nonlinear systems including superfluids, fiber optics, plasmas and Bose-Einstein condensates. Modulation instability in the NLSE is also a significant current area of study in the context of understanding the emergence of high amplitude or high intensity events that satisfy "rogue wave" statistical criteria. Here, exploiting recent advances in real time ultrafast optical metrology via an optical time lens system, we perform real-time measurements in an NLSE optical fibre system of the unstable breakup of a continuous wave field, simultaneously characterising emergent modulation instability breathers, and their associated statistics. Our results allow quantitative comparison between experiment, modelling, and theory, and we show very good agreement in both extracted intensity profiles and associated statistics.

Precision frequency metrology and attosecond pulse generation critically rely on stabilization of the carrier-envelope phase (CEP) of mode-locked lasers. So far, only a relatively small class of lasers has been successfully stabilized to warrant phase jitters of a few hundred milliradians as they are required for the generation of an isolated attosecond pulse. For stabilizing certain laser types, the exact reasons for the observed difficulties (or the lack thereof) is only poorly understood. Here we compare the free-running CEP noise of four different lasers, including a femtosecond Ti:sapphire laser and three mode-locked fiber lasers. This study indicates a correlation between amplitude and frequency fluctuations at low Fourier frequencies for essentially all lasers investigated. This finding is well explained with technical noise sources and thermal coupling mechanisms below the upperstate lifetime of the laser gain material. However, for one of the lasers under test, we observe a broadband amplitude-to-phase coupling mechanism well above the upperstate lifetime. This coupling mechanism is related to a dynamical loss modulation. We verify our explanation by numerical simulations, which identify resonances of the saturable absorber mirror as a possible explanation for the coupling mechanism. In case of high modulation depth and resonantly enhanced saturation characteristics, such a saturable absorber can give rise to broadband conversion of spontaneous emission amplitude noise into phase noise, which may cause, in turn, extremely broadband noise signatures, exceeding a megahertz bandwidth.

We report an optical pulse profiling method which has a potential to enable real-time stamping of optical pulse waveforms to corresponding characteristic spectra without any user's expertise and skills. Its performance was confirmed by comparison with the conventional matured measurement tools and was as accurate as the conventional ones. The concept can be extended for real-time measurement of pulse-by-pulse phenomena provided the use of fast spectrum analyzers enables to acquire and storage pulse-by-pulse spectrum in real-time.

Single-shot and long record length spectrum measurements of high-repetition-rate optical pulses are essential for research on nonlinear dynamics as well as for applications in sensing and communication. To achieve a continuous measurements we employ the Time Stretch Dispersive Fourier Transform. We show single-shot measurements of millions of sequential pulses at high repetition rate of 1 Giga spectra per second. Results were obtained using -100 ps/nm dispersive Fourier transform module and a 50 Gsample/s real-time digitizer of 16 GHz bandwidth. Single-shot spectroscopy of 1 GHz optical pulse train was achieved with the wavelength resolution of approximately 150 pm. This instrument is ideal for observation of complex nonlinear dynamics such as switching, mode locking and soliton dynamics in high repetition rate lasers.

Ultrashort pulses emerging from multimode optical fibers are spatiotemporally complex—the multiple fiber modes have different spatial shapes and different propagation velocities and dispersions inside fibers. To measure the complete spatiotemporal field from multimode fibers in real time, we propose and demonstrate a technique for the complete measurement of these pulses using a simple pulse characterization technique, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). It yields the complete electric field vs. space and time from multiple digital holograms, simultaneously recorded at different frequencies on a single camera frame.

The real-time measurement of fast non-repetitive events is arguably the most challenging problem in the field of instrumentation and measurement. These instruments are needed for investigating rapid transient phenomena such as chemical reactions, fast physical phenomena, phase transitions, protein dynamics in living cells and impairments in data networks. Optical spectrometers are the basic instrument for performing sensing and detection in chemistry, physics and biology applications. Unfortunately, the scan rate of a spectrometer is often too long compared with the timescale of the physical processes of interest. In terms of conventional optical spectroscopy, this temporal mismatch means that the instrument is too slow to perform real-time single-shot spectroscopic measurements. Single-shot measurement tools such as frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are, although powerful, therefore unable to perform pulse-resolved spectral measurements in real time.

RogueScope is a commercially available single-shot optical spectrometer with a frame rate of up to Billion frames per second, at least tens of thousand times faster than the next fastest spectrometer. The RogueScope real-time capability is enabled by photonic time-stretch implemented by Time-Stretch Dispersive Fourier Transform. The RogueScope can capture large data sets to reveal rare events with meaningful accuracy. Applications include optical rouge waves, laser transients, chemical reactions, and nonlinear dynamics. RogueScope is an essential tool for measurements of fast stochastic processes such as laser transients, rare events and outliers in optical systems. RogueScope is ideal for capturing non-Gaussian statistics that are signatures of complex dynamics.

Stimulated Raman scattering spectroscopy is a powerful technique for label-free molecular identification, but its broadband implementation is technically challenging. We introduce and experimentally demonstrate a novel approach based on photonic time stretch. The broadband femtosecond Stokes pulse, after interacting with the sample, is stretched by a telecom fiber to 15ns, mapping its spectrum in time. The signal is sampled through a fast analog-to-digital converter, providing single-shot spectra at 80-kHz rate. We demonstrate 10^-5 sensitivity over 500 cm-1 in the C-H region. Our results pave the way to high-speed broadband vibrational imaging for materials science and biophotonics.

Broadband Laser Ranging (BLR) is a new diagnostic being developed in collaboration across multiple USA Dept. of Energy (DOE) facilities. Its purpose is to measure the precise position of surfaces and particle clouds moving at speeds of a few kilometers per second. The diagnostic uses spectral interferometry to encode distance into a modulation in the spectrum of pulses from a mode-locked fiber laser and uses a dispersive Fourier transformation to map the spectral modulation into time. This combination enables recording of range information in the time domain on a fast oscilloscope every 25-80 ns. Discussed here are some of the hardware design issues, system tradeoffs, calibration issues, and experimental results. BLR is being developed as an add-on to conventional Photonic Doppler Velocimetry (PDV) systems because PDV often yields incomplete information when lateral velocity components are present, or when there are drop-outs in the signal amplitude. In these cases, integration of the velocity from PDV can give incorrect displacement results. Experiments are now regularly fielded with over 100 channels of PDV, and BLR is being developed in a modular way to enable high channel counts of BLR and PDV recorded from the same probes pointed at the same target location. In this way instruments, will independently record surface velocity and distance information along the exact same path.

Broadband laser ranging (BLR) is essentially a spectral interferometer used to infer distance to a moving target. The light source is a mode-locked fiber laser, and chromatic dispersion maps the spectral interference pattern into the time domain, yielding chirped beat signals at the detector. A BLR record is a sequence of these chirped signals, representing consecutive target positions. To infer distance to a target, each underlying pulse envelope must be consistently registered and subtracted despite environmentally-induced variability. Then, nonlinear transformation of the phase is applied to remove the chirp, an FFT is performed to determine the peak frequency of the de-chirped signal, and a calibration factor relating de-chirped frequency to distance results in target position. Here, these analysis steps are discussed in detail.

An ultra-intense short pulse laser induces a shock wave in material. The pressure of shock compression is stronger than a few tens GPa. To characterize shock waves, time-resolved velocity measurement in nano- or pico-second time scale is needed. Frequency domain interferometer and chirped pulse laser provide single-shot time-resolved measurement. We have developed a laser-driven shock compression system and frequency domain interferometer with CPA laser. In this paper, we show the principle of velocity measurement using a frequency domain interferometer and a chirped pulse laser. Next, we numerically calculated spectral interferograms and show the time-resolved velocity measurement can be done from the phase analysis of spectral interferograms. Moreover we conduct the laser driven shock generation and shock velocity measurement. From the spectral fringes, we analyze the velocities of the sample and shockwaves.

The general theory of first-order spatiotemporal distortions provides a very helpful framework for understanding beam couplings in ultrashort pulses. The theory describes both real and imaginary coupling terms between 4 pairs of dimensions. The imaginary coupling terms are difficult to understand and visualize because they are difficult to plot in a meaningful way. In general, plotting the spatiotemporal intensity and phase of pulses in in two and three dimensions is a difficult problem. Our work on pulse visualization provides an unprecedented opportunity to study spatiotemporal couplings in ultrashort pulses. We create movies of pulses as they would appear naturally, with all of their evolving spatial, temporal, and spectral structure readily apparent.

We developed a unique time-lens configuration for measuring in real time the temporal evolution of Rogue waves in optical fibers. Our time-lens configuration is based on array of several time-lens and we obtain the temporal evolution of Rogue waves by super-resolution techniques similar to a 3D imaging by a lens array.

The experimental and calculated results as well as the theoretical background will be presented.

We investigate the polarization of supercontinuum generated in nominally non-birefringent silica photonic crystal fibers over the entire spectrum of the source (450-2400 nm). We demonstrate that the degree of polarization varies over the spectrum but that some parts of the spectrum show stable polarization extinction ratios (PER) of over 10 dB. We experimentally demonstrate how the spectrally resolved polarization develops with increasing power and along the length of the nonlinear fiber. The experimental results are compared to numerical simulations of coupled polarization states mimicking the experimental conditions. Subsequently, a single-shot pulse-to-pulse polarization dependent relative intensity noise (PD-RIN) was measured and the noise characteristics were analyzed using long-tailed and rogue wave statistics. To do this, we used a range of 10 nm narrow bandpass filters (BPF) between 550 nm to 2200 nm, and fast photo detectors, to record 800 consecutive pulses. Peaks from these pulses are first extracted, then distribution of their pulse height histogram (PHH) is constructed. Analysis using higher-order moments about the mean (variance, skewness and kurtosis) showed that: (1) around the pump wavelength of 1064nm, the PD-RIN is lowest, PHH exhibits a Gaussian distribution, and higher order moments are zero, (2) further away from pump, PD-RIN increases in parabolic fashion, PHH follows a left-skewed long-tailed Gamma distribution, and higher-order moments increase. Spectrally, the difference of the PD-RIN in the two orthogonal axes increases with PER.

Ghost imaging is an optical technique that produces the image of an object by correlating the total amount of light transmitted through the object with the random intensity pattern that the object is irradiated with. When the technique is used with incoherent light sources, characterized by random temporal intensity fluctuations, it requires recording a very large number of distinct realizations to obtain a faithful image reproduction. In order to significantly reduce the number of realizations, one can use pre-programmed known patterns, so-called computational ghost imaging.

Recently, ghost imaging was transposed into the time-domain to image ultrafast varying waveforms. Here, we report on a novel proof-of-concept experiment of computational ghost imaging in the time domain using wavelength multiplexing. By encoding different time-varying intensity patterns onto separate wavelength channels, we can perform simultaneous measurement of multiple realizations. This allows us to perform ghost imaging in real-time, without the need of probing the time-varying object repeatedly. Specifically, we use a programmable spectral filter to encode a set of 32 Hadamard-like time-varying intensity patterns onto a broadband LED light source. An electro-optic intensity modulator driven by an electrical waveform is used to create the time-varying object to be measured. The object is then reconstructed “blindly” by correlating the time-averaged transmission of each wavelength channels with the digitized form of the time-varying Hadamard patterns that illuminate the object. The temporal resolution of the measurement is currently to 0.5 s limited by the speed at which the variable spectral filter can be manipulated.

The generation of clean solitons is important for a number of applications such as optical analog-to-digital conversion (ADC) based on soliton self-frequency shift. In real sources the quality of the pulses is deteriorated by dispersive waves, continuous wave (CW), amplified spontaneous emission (ASE). The dispersive waves appear in the spectral profile as side-lobe components that would limit the resolution of ADC. Spectral compression techniques cause the appearance of a pedestal on the spectrum. All of these imperfections of pulses have to be eliminated to improve the performance of alloptical systems. The nonlinear optical loop mirror (NOLM) is a good candidate for these tasks. In the present work we report the implementation of a polarization-imbalanced NOLM for soliton cleaning. The NOLM consists of a nearly symmetrical coupler with a 51/49 coupling ratio, 100 m of twisted OFS Truewave fiber whose dispersion value is 9 ps/nm/km at 1550 nm, and a tunable in-line fiber polarization controller (PC) asymmetrically inserted inside the loop. The use of the nearly symmetrical coupler allows very low transmission for low power components of radiation. At the same time adjustment of the PC allows the adjustment of the nonlinear characteristic to have a maximum transmission for solitons with different durations. We used two sources of pulses, SESAM based and a ring fiber laser. At the appropriate adjustment of PC, we obtained a rejection of ASE by 220 times, rejection of the dispersion waves and the pedestal by more than 200 times. The maximum transmission reached 70%.

A diagnostic method is presented that enables single shot characterization in amplitude and phase of ultrashort, weak pulses. The method is particularly well adapted to the characterization of pulses generated by optical parametric oscillators.

The accuracy of timing jitter is of prime importance in the prevalent utilization of Light Detection and Ranging (LiDAR) technology for the real-time high-resolution three-dimensional (3D) image sensor, especially for relatively small object detection in various applications, such as in the fully automated car navigation and military surveillance. To assess the accuracy of timing, that is, the accuracy of the distance or three-dimensional shape, the standard deviation method can be used in the Time-of-Flight (ToF) LiDAR technology. While most timing jitter analyses are mainly based on a fiber-network or open space at a relatively short range distance, more accurate analyses are required to extract more information about the timing jitter at in a 3D image sensor long-range free space conditions for extended LiDAR-related applications.

In this paper, utilizing a Single-Shot LiDAR System (SSLs) model with a 400 MHz wideband InGaAs Avalanche Photodiode and a 1550 nm 2 nsec full width at half maximum MOPA fiber laser, we analyzed the precise timing jitter for the implemented SSLs to characterize the measurement results. Additionally, we report the enhanced results for the resolution and precision in the given SSLs using the spline interpolation method from the measured results, and multiple-shot averaging (MSA). Finally, by adapting the proposed method to an implemented high resolution 3D LiDAR prototype, called the STUD LiDAR prototype, which can be understood as one kind of SSLs because it has a single source and a single detector as in a SSLs, we observed and analyzed the 3D resolution enhancement.

Reservoir Computing is a bio-inspired computational paradigm particularly well adapted to time-dependent signal processing. The past years have seen the realisation of photonic reservoir computers with performance comparable to digital algorithms. Most of these works are based on delay dynamical systems in which the photonic neurons are treated sequentially. We have recently realised an experimental system based on the concept of frequency multiplexing, in which the neurons are materialised as the amplitude of light at different frequencies. In this system the neurons are processed in parallel, making it in principle much faster than the sequential systems. In most of the works up to now the output of the reservoir is implemented using slow digital offline post-processing. This is also the case of our recent experiment on frequency parallelism. Here we demonstrate, using numerical simulations, the possibility of an analogue electronic readout layer for this system. Our simulations take into account all the experimental limitations of the setup, e.g. sampling rates, device bandwidths, resolutions, and noise. The results obtained are comparable to those produced with the same architecture and a digital output layer. The proposed setup is thus an important step towards analog, low footprint, all-optical information processing. Moreover parallel processing will be necessary for high bandwidth applications.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews